Conventionally, a Ni-base superalloy is used as a material of rotor blades and stator vanes, which is a high temperature member such as aircraft engines or gas turbine engines. The Ni-base superalloy has γ (gamma) matrix which is an austenite phase and γ′ (gamma prime) phase which is an ordered phase dispersed and precipitated in the matrix. The γ′ phase mainly comprises an intermetallic compound represented by Ni3Al, and due to the presence of this γ′ phase, high temperature strength of a superalloy is improved.
Raising a combustion gas temperature is most effective to increase efficiency of gas turbine engine, and for this reason, a Ni-base superalloy having further excellent high temperature strength is desired. A conventionally cast Ni-base alloy, a directionally solidified Ni-base superalloy and a Ni-base single crystal superalloy are realized by the compositional ratio of an alloy and the improvement of production process. In recent years, a Ni-base single crystal superalloy and a directionally solidified Ni-base superalloy, having compositional ratio of Re (rhenium) exceeding 5 wt %, that are called a third generation superalloy are developed (Patent Document 1), but had the problem that when solid solution amount of Re into γ phase exceeds the limit, a so-called TCP phase (Topologically Close Packed phase) is precipitated at high temperature, resulting in deterioration of high temperature properties. Furthermore, development of a Ni-base single crystal superalloy and a directionally solidified Ni-base superalloy of fourth and fifth generations is carried out by adding a platinum group element such as Ru (Ruthenium), thereby suppressing formation of TCP phase and attempting to improve high temperature strength (Patent Document 2).    Patent Document 1: U.S. Pat. No. 4,643,782    Patent Document 2: U.S. Pat. No. 6,929,868